I have two machines, one is a master(running roscore) and the second is a slave. Until now I set manually the time for each computer. Now, I want to do set it automatically. I searched a lot of options in the internet but I couldn't configure well the configurations. I tried chrony,ntp,ntpdate and nothing happened. I think that our ISP is blocking the access for these ntp servers. I also tried to get the time from the ntp server of our ISP but I think that I don't understand very well this subject. I want to know if there is a simple tutorial how I can take the ros time from the master to be on the slave machine. I prefer to not use a ntp server. I believe that there is a simple way to do that.